So, Kikei of Collision guild brought this to my attention. As a monsters level increases, your defensive stats are capped:
Level 50: 70.00%
Level 51: 66.66%
Level 52: 63.49%*
Level 53: 60.42%*
Level 54: 57.58%*
*These are just guesses based on the pattern shown for level 50/51 tooltip.
What does this mean? The true cap for Defense, Parry, and (probably) Dodge is 3058 points (this value is the 70% rate against level 50 mobs). Any points above that are wasted, as shown in the image.
Why didn't anyone notice this before? Because the AoD parry rate bonus can overcome this cap, since it is calculated after the cap, similar to the Parrying skill. So, on my tooltip, it always showed 70% against level 51 mobs; even though the true cap is 66.66%, with the AoD Parry rate bonus, it boosted it to 70% (which seems to be the tooltip cap). Without the ability to see the tooltip for level 52+ mobs, the numbers above are just guesses.